This disclosure relates in general to immersion probes and, but not by way of limitation, to using immersion probes for measuring the water-cut in gas-condensate (wet-gas) wells, amongst other things.
Probes, such as immersion probes, can offer a range of data which aids in both determining and helping to regulate the content and/or flow rate of gas and oil flows in wells. Use of these probes varies dependent on the type of well in which it is utilized. For instance, natural gas and crude oil wells vary in the amount of gas-condensate, oil, natural gas, water and gas volume fractions (GVF) that are present. Accordingly, the probes are designed to accommodate such differences in order to provide the most accurate readings of the constituents within each well type.
Currently, the primary optical technique for determining the water-cut is utilizing a near infrared (NIR) beam to measure absorption levels in the multi-phase mixtures for oil/gas-condensate wells having low to high gas volume fractions. Water-cut may also be referred to as water-in-liquid ratio (WLR) for a well-mixed liquid and is the amount of water content in the liquid phase of a multiphase flow. The NIR beam is utilized because water is highly absorbed in the NIR range, with one of the peak absorptions at around 1450 nanometers (nm). The absorption of oils, condensate and water mixtures varies, each can have relatively different absorptions at different wavelengths. For instance, oil-condensate or light oils show higher absorptions at lower wavelengths and water shows absorption peaks at higher wavelengths.
Prior art configurations for determining the water cut of a flow, use a probe disposed along the two opposing sides of a well pipe and having a beam sent across the pipe from an NIR and/or ultraviolet (UV) light source to a receiving element separated by the diameter of the pipe. The received light is then sent to an NIR and/or UV spectrometer and the results are processed by a computer or other device having a capability to perform spectral analysis. The spectrally analyzed results from the aforementioned configuration, which configuration is disclosed in the commonly owned GB Patent Number GB2426579B, provide for analyzing the presence of water and/or oil condensate in the liquid phase of gas-condensate multi-phase wells. As previously mentioned, the near infrared light at a selected wavelength band is highly absorbed by water, and has close to zero absorption by the gas and gas condensate. The UV light at a selected wavelength band, on the other hand, is highly absorbed by condensate oil and is substantially transparent to the gas and water.
The aforementioned technique is limited to sensing the liquid fractions across the diameter of a pipe for flows of very high GVF or very low liquid fractions, as well as provides presence of water and/or oil condensate in a multiphase flow. However, the actual quantitative water-cut measurements can be problematic in these systems as GVF decreases or as the liquid fraction increases. This is primarily due to the increased scattering attenuation effect cross pipe which may overwhelm the underlying small absorption measurements used to extract liquid fractions. The scattering effect occurs from entrained liquid droplets and bubbles within the gas phase flow and liquid phase flow, respectively. Further, additional problems occur when the light source is inconsistent. In some systems, the light sources are integrated into the insertion sensing probe itself and exposed directly to the high temperature and pressure conditions of the flows in a well pipe. These light sources, such as light emitting diodes (LED), become degraded and produce shifted wavelength bands at different temperatures and over the lifetime of the device. Accordingly, such faulty light sources require removal and replacement of the entire sensing probe system.